Attach weapon to hands, left hand unsynchronized

I have full animation character with aimoffset and holding weapon animation, I have this problem when the hands moving and there is unsynchronized between my hands and the weapon.
I searched about this problem and I found the way to fix this is using IK bones nodes which I did, but eventually it ends up by not rotating at all or its rotating the bones extremly uncorrectly.
How can I fix this problem? I have to keep taking parameter constantly and update bones?
Attached few images describing the problem, also Node IK which I tried to do but it’s not working.

I used this tutorial UE4 Tutorial: The Right Way to Do Left-Hand Weapon IK – Zag's Blog
In order to solve this.

TY so much this info.